This invention relates to a novel process for producing heat-resistant semi-inorganic compounds.
Known methods for producing organoborosiloxane compounds, a kind of the semi-inorganic compounds, include, for example, the dehydrocondensation reaction of boric acid with a silanediol, the dehydrochlorinating condensation reaction of boric acid with diorganodichlorosilane, the dealcoholizing condensation reaction of boric acid with a diorganodialkoxysilane, and the de-esterifying condensation reaction of a boric ester with a diorganodialkoxysilane. U.S. Pat. No. 2,517,945 discloses a method for producing an organoborosiloxane compound, a linear polymer, which comprises reacting a difunctional boronic acid such as benzeneboronic acid used instead of boric acid which is trifunctional, with diphenylsilanediol at a temperature of 170.degree. to 260.degree. C.
Previously, the present inventors found that an organoborosiloxane polymer having at least one phenyl group bonded to a silicon atom had much better heat resistance than those organoborosiloxane compounds which had been known up to that time, and disclosed the phenyl-containing organoborosiloxane polymer and a method for its production in U.S. Pat. application Ser. No. 835,373 filed Sept. 21, 1977, now Pat. No. 4,152,509. The heat resistance of the phenyl-containing organoborosiloxane polymer is believed to be attributed to its three-dimensional network structure. However, it has the defect that when a high degree of network structure is imparted to the polymer to increase its heat resistance, the softening point of the organoborosiloxane polymer increases extremely, and it is difficultly soluble in a solvent, and therefore, its processability is reduced at the time of using it as a raw material for a heat resistant material. Accordingly, the phenyl-group containing organoborosiloxane polymer which the present inventors previously suggested is not entirely satisfactory.
The present inventors made extensive investigations, and found that a semi-inorganic compound having a borosiloxane bond which has superior heat resistance and is readily soluble in solvent can be obtained by reacting an organoborosiloxane compound with at least one specified organic compound selected from the group consisting of aliphatic polyhydric alcohols, aromatic alcohols, phenols and aromatic carboxylic acids. This discovery has led to the present invention. Since the semi-inorganic compound obtained by the novel process is readily soluble in a solvent, it has very good processability and is useful as a raw material for various heat-resistant materials.